The earlier English uses of spirit are mainly derived from passages in the Vulgate, in which spiritus is employed to render Gr. pneuma and Heb. ruax (both meaning 'breath'). The translation of these words by spirit (or one of its variant forms) is common to all English versions of the Bible from Wyclif onwards.

Soul is common Germanic, and is generally used in situations where today we would use words like personality, character, mind -- or spirit, to refer to the way people behave and our intuitions about "what they're really like".

So, if one is sufficiently abstract, yes, they can be synonymous. But beware of specific uses, which are highly idiomatic.

I think what you're really saying here is that "soul" and "spirit" each have multiple definitions, some of which are synonyous and some of which are not. Life if we say, "Humans have an immortal soul", and "Bob likes soul food", we are using two different definitions of the word.
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JayJul 27 '12 at 17:56